Add missing _rec_name

issue2189
review162001
(transplanted from 5b262957935337c771e34d32285486e7e90669d4)

product.py

@@ -9,6 +9,7 @@ class ProductCostHistory(ModelSQL, ModelView):
     'History of Product Cost'
     _name = 'product.product.cost_history'
     _description = __doc__
+    _rec_name = 'date'
 
     template = fields.Many2One('product.template', 'Product')
     date = fields.DateTime('Date')